The invention relates to an actuator for steering rear wheels which may find its application in axially driving a steering shaft, by connection therewith, in order to assist a steering of an automobile, for example.
To realize a four wheel steering system for an automobile, for example, there is a need to provide an actuator for steering rear wheels which is operative to drive a steering shaft for the rear wheels in the axial direction thereof. To realize a high precision in controlling the steer angle, it is desirable to use such actuator which can be electrically driven.
Accordingly, an actuator for steering rear wheels of the kind described conventionally comprises an electric motor, a reduction gearing connected to the output from the motor, and a converter mechanism which transmits a rotary motion, outputted from the reduction gearing, to a steering shaft as converted into a linear motion.
Such actuators are known in the art, as disclosed in Japanese Laid-Open Patent Applications No. 154,955/1985, No. 206,782/1985, No. 103,763/1988, No. 330,445/1993, and No. 330,446/1993 and Patent Publication No. 502,591/1992 (International Laid-Open No.: WO90/03,910).
An actuator for driving rear wheels, which is available in the art, is bulky in size and complex in construction, requiring time and labor for assembly during the manufacturing and thus resulting in a high manufacturing cost. However, it is very difficult to reduce the size of such actuator. By way of example, while a reduction in the size of the electric motor is indispensable in order to reduce the size of such actuator, the heating effect which occurs when the motor is driving is likely to cause a failure by a temperature rise inasmuch as a motor having a reduced size must be housed in an enclosed space of limited volume.